The method according to the invention has the advantage that even when the engine is at rest, i.e. when it is not running, the pressure of the fuel is increased in relation to the normal pressure, which prevents the formation of vapor bubbles from the start. In contrast to the prior art, therefore, the method according to the invention does not rinse already existing gas bubbles out of the fuel lines, but rather prevents them from forming in the first place. This makes it possible to supply fuel to the combustion chambers of the engine even faster during the starting process, which accelerates the starting process itself and improves the starting behavior of the engine.
Increasing the fuel pressure in the fuel line only when the engine is not operating also has the advantage over a continuously elevated fuel pressure that the components of the engine are under less stress during normal operation. This applies in particular to the fuel pump, whose service life is extended by the lower normal pressure and also applies to the fuel lines, which are less susceptible to permeation at the lower normal pressure.
Advantageous modifications of the invention are disclosed in the dependent claims.
A first modification provides that the pressure of the fuel, at least in the above-mentioned region of the fuel line, is increased when the engine is not running if the temperature of the engine is above a limit value. The formation of vapor bubbles is particularly likely when the fuel in the fuel lines is warm. Such a heating of the fuel is in turn to be expected when the engine is switched off after a long period of operation and due to heat dissipation, the hot engine heats the fuel line, the fuel pump, and/or other elements of the fuel system.
The modification of the method according to the invention, takes into account this heating of the fuel. On the other hand, the increase of the fuel pressure in the fuel line is also eliminated when the engine is not running if, for example, the engine is started for only a short time, i.e. it has not reached a high operating temperature and therefore no vapor bubble-inducing heating of the fuel in the fuel line is to be expected.
The invention also proposes that the pressure of the fuel in the above-mentioned region of the fuel line remain elevated at least during the starting of the engine and preferably during a time interval after the starting of the engine. This accelerates a reliable starting of the engine even more and, with a high degree of reliability, assures a smooth and safe operation of the engine after the starting procedure.
It is particularly preferable if the period of time during which the pressure of the fuel remains elevated after the starting of the engine, at least in the above-mentioned region of the fuel line, depends on the temperature of the engine. As explained above, the probability of the formation of vapor bubbles depends on the temperature of the fuel, which in turn depends on the temperature of the engine. During operation of a very hot engine, for example an engine that is started again after a long period of operation followed by a short intermediary stop, the danger of vapor bubbles being produced is particularly pronounced. In this instance, the pressure of the fuel should remain elevated for a particular time interval, which depends on the temperature of the engine. If need be, the pressure can be reduced again when the temperature of the engine has fallen below a limit value.
In a particularly preferred modification of the method according to the invention, a high-pressure region and a low-pressure region of the fuel line are connected to each other during the phase with the increased pressure of the fuel, at least in a region of the fuel line, particularly when the engine is not running. Such a fuel line with a high-pressure region and a low-pressure region is used, for example, in internal combustion engines with gasoline direct injection.
In a fuel system of this kind, the fuel is first delivered by an electric fuel pump into the low-pressure region of the fuel line and is supplied to a high-pressure pump directly driven by the engine. This high-pressure pump delivers the fuel at very high pressure (up to 120 bar) into a fuel accumulation line, which is also referred to as a “rail”. From this rail, the fuel is supplied directly to the injection valves, which inject the fuel directly into the combustion chambers of the engine.
Normally when the engine is not running, the high-pressure region and the low-pressure region of the fuel line are separated from each other. The high-pressure components of a high-pressure region, e.g. the high-pressure pump, the high-pressure injection valves, a quantity control valve, and a pressure control valve, are sometimes subjected to the high pressure in the high-pressure region for a very long period of time. If the high-pressure region is connected to the low-pressure region during the phase with the increased pressure of the fuel, this automatically results in a reduction of the pressure in the high-pressure region to a common pressure value, which is, however, higher than the usual pressure value in the low-pressure region of the fuel line, thus preventing vapor bubbles.
The components in the high-pressure region of the fuel line are consequently no longer subjected to the particularly high pressure so that the sealing demands on these components are reduced. This reduces the production costs for the corresponding components and possibly also increases the service life of these components.
One possibility for increasing the pressure of the fuel in the above-mentioned region in the above-mentioned manner is comprised in that a device, which sets the pressure of the fuel to a normal level, at least in the above-mentioned region of the fuel line, is switched off during the phase with increased fuel pressure. This variant of the method according to the invention is particularly easy to achieve.
It is also possible for the increase of the pressure of the fuel, at least in the above-mentioned region of the fuel line when the engine is not running, to include the activation of at least one fuel pump after the engine is switched off. Such an activation of the fuel pump is very easy to achieve and contributes to the desired result.
It is also possible for the increase of the pressure of the fuel, at least in the above-mentioned region of the fuel line when the engine is not running, to take place at least by means of a temperature increase of the fuel in the above-mentioned region of the fuel line. This variant of the method according to the invention takes advantage of the increase in the temperature of the fuel that is expected anyway: heat dissipation from the hot engine can cause such a temperature increase, which due to the closed volume of the fuel in the fuel line, causes the desired pressure increase. In this modification of the method according to the invention, therefore, the pressure increase is produced in a particularly simple manner.
The invention also relates to a computer program, which is suitable for executing the above-mentioned method when it is run on a computer. It is particularly preferable if the computer program is stored in a memory, in particular a flash memory.
The invention also relates to a control and/or regulating unit for operating an internal combustion engine, in particular of a motor vehicle, in which at least one fuel pump delivers the fuel from a fuel tank into a fuel line and in which the pressure of the fuel, at least in a region of the fuel line, is increased as a function of an operating state. Such a control and/or regulating unit is known from the market. In order to accelerate the starting process of the engine, the invention proposes that the control and/or regulating unit be suitable for controlling and/or regulating the above-mentioned method. It is particularly preferable if the control and/or regulating unit is provided with a computer program of the above-mentioned type.
The invention also relates to an internal combustion engine with at least one fuel pump that delivers fuel into a fuel line and with a device that can increase the pressure of the fuel, at least in a region of the fuel line, as a function of an operating state of the engine. An internal combustion engine of this kind is also known from the market. In order to be able to start this engine better, the invention proposes that it be provided with a control and/or regulating unit of the above-mentioned type.
In the engine according to the invention, in order to be able to produce the simplest possible pressure increase of the fuel pressure in the fuel line that can be achieved with the control and/or regulating unit, the invention proposes that the engine have a first pressure adjusting device, which can adjust a normal pressure of the fuel, at least in a region of the fuel line.
The invention also proposes that the engine have a second pressure adjusting device that can adjust an increased pressure of the fuel, at least in the above-mentioned region of the fuel line; the first and second pressure adjusting device are each connected at least to the above-mentioned region of the fuel line. In addition, the engine should also have a device that can fluidically disconnect the first pressure adjusting device at least from the above-mentioned region of the fuel line when the engine is not running.
The assembly of the above-mentioned components is simplified by virtue of the fact that the pressure adjusting devices and the disconnecting device are integrated into a module.